# Full text of "Text Book Of Mechanical Engineering"

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```Time and Distance Bases.

491

velocity for the given position of crank, while the crank arm itself
gives W's velocity. Taking various positions of P on HJ, and
setting up the corresponding polar radii, the curve of P's velocity
is obtained as H K j, while the ordinates A w, set up dotted on a
base N o of half crank circle circumference, shew crank velocity.

4

Assuming P's pressure as uniform, the ordinates Im will give
a curve of pressure; and the AE ordinates, being transferred from
the polar curve to the base N o,. will give a curve of tangential
pressures on crank. Notice points Q R and s T, where P and W
have equal velocities, and also points F and w, where P has its
highest velocity, and W its greatest pressure

Time and Distance Bases.—The pfofile of velocity
curve depends on the terms in which we state the base-line
divisions. The curves in Fig. 434 are drawn with a time base
line (equal titties), but the oblique lines at c and D -would be
parabolas if a distance base (equal distances) were used. In
Fig* 453, K j is a distance base, but supposing NO to represent

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